1. Field of the Invention
The present invention relates to an apparatus and method for supplying power in a semiconductor memory device, and more particularly, to an apparatus and method for supplying power in a semiconductor memory device, capable of controlling voltage supplying time in accordance with power consumption.
2. Discussion of Related Art
Most circuits use an apparatus for supplying power. An apparatus for supplying power used in a memory device thereof will be described as follows.
A sense amplifier included in a semiconductor memory device is used for many objects, and it is also used to amplify voltage difference of a pair of bitlines. Especially, in DRAM, the sense amplifier amplifies the voltage difference of a pair of bitlines, performing a data read/write operation and a data refresh operation of a memory cell. Thus, many operations of the sense amplifier are controlled by an additional sense amplifier control circuit.
In other words, as a semiconductor memory device has been integrated higher and used lower power, and an operation voltage has been lower, there has been studied about technical assistance to stand by the operation of the sense amplifier of the memory device, of which is a method of overdriving of the sense amplifier.
In a pull-up operation from a precharge voltage to an internal voltage, the internal voltage is generally lower. Here, because there is not much differences between the internal voltage and the precharge voltage, it takes long time to rise up the internal voltage to a target level (the internal voltage). To overcome the problem, an external voltage which is relatively high level is supplied by an apparatus for supplying power during a predetermined period, which is called as an overdriving.
For more detailed description, when the sense amplifier is activated, a relatively high external voltage (i.e., 3.3V) is supplied to improve data sensing speed of the sense amplifier, and then an internal voltage (i.e., 2.2V) is supplied to maintain the voltage of the sense amplifier.
During this, an apparatus for supplying power is necessary to supply the external voltage only during a predetermined period. Accordingly, it will be described about a structure or an operation of an apparatus for supplying power in accordance with the conventional technique as follows.
FIG. 1 is a schematic diagram of a circuit illustrating an apparatus of supplying power in accordance with the conventional art.
Referring to FIG. 1, an power supply apparatus 100 is comprised of a pulse generator 110 and an internal voltage generator 120 for applying a relatively high external voltage VDD to a sense amplifier 130 for a predetermined period (hereinafter, referred to as 'overdriving period) at the beginning operation, and then for supplying an internal voltage Vcore.
In the aforementioned FIG. 1, the pulse generator 110 is operated by an enable signal ACT which becomes high level when an active command is inputted, and generates an overdriving signal ovdb only during the overdriving period. As a result, it leads a switching device P10 connected to an external voltage terminal to be turned on. When the switching device P10 is turned on, the external voltage VDD is supplied to the sense amplifier 130 only during the overdriving period.
During this state, the external voltage VDD is applied to the sense amplifier 130 which is selected by first and second sense amp driving signal SAP1 and SAN1. According to this, a voltage precharged to an input terminal of the sense amplifier 130 begins to rise in a rapid speed.
And then, when the overdriving period is completed, the switching device P101 is turned off by the overdriving signal ovdb of the pulse generator 110. As a result, the sense amplifier 130 is applied the internal voltage Vcore generated from the internal voltage generator 120, instead of the external voltage VDD. During the aforementioned operation, when a pair of bitlines is selected, power consumption is not much, so that there is no problem. However, when the n-numbered pair of bitlines is selected such as a refresh operation, current consumption is increased more than n times.
Therefore, in the refresh operation, because the currents are consumed a lot at a completing timing of the overdriving period, if the external voltage VDD is not supplied and a relatively low internal voltage is supplied at the completing timing of the overdriving period, there is not a normal operation performed.
In order to solve the aforementioned problems, during the refresh operation, a plurality of internal voltage generators should be operated, and also should be comprised of a plurality of internal voltage generators in the power supply apparatus 100. It accordingly causes other problems.